L = {a^i b^i | i >= 0, j >= 0}
Given m = 4 and word selection of aabb an xyz can be selected of 'a' 'ab' and 'b'. Correspondingly I can 'pump' ab to abab making aababb which is not in my language that may suggest non-regularity.
What did I prove or not prove - explain your answer as related to what we know about application of P.I.